Fig. 1.

Characterization of S, trehalose, and their mixtures used to manufacture films for seed coating. (A) Molecular dynamics simulation of S when exposed to water (black dots) and to a water and trehalose solvent matrix (red dots); root-mean-squared deviation (RMSD) measures average distance between the atoms. The 3 insets depict S structure after relaxation and at the end of the simulation (40 ns) in the different media. (B) Circular dichroism (CD) of suspensions of S and mixtures of S and ST. The disaccharide has no impact on the protein random coil conformation in water suspension as indicated by the negative bands near 195 nm and low ellipticity above 210 nm. (C) Dynamic light scattering (DLS) analysis of S nanomicelles aggregation in water as a function of trehalose concentration. The average diameter of silk nanomicelles was not affected by trehalose concentration in the water suspension. Error bars indicate SD. (D) Fourier transform infrared spectroscopy (FTIR) spectra of films obtained by drop casting of S, trehalose (T), and their mixtures (ST). The random coil-dominated resonance peaks of the amide bonds in the amide I and amide III regions were not affected by the presence of trehalose, indicating that the disaccharide has no effects on the protein polymorphism during the sol–gel-solid transition. In the Right, FTIR spectra show that a polymorphic random coil to β-sheet transition of S can be induced post film formation with water annealing as evidenced by the appearance of a peak at 1,621 cm⁻¹. (E) Mechanical properties of films consisting of S, trehalose, and their mixtures investigated with nanoindentation. Trehalose concentration and water-annealing postprocess resulted in an increase in hardness and apparent modulus and in the formation of more brittle films. Error bars indicate SD.